The invention relates to a method for starting an internal combustion engine operated with gasoline direct injection. The engine is subdivided into several cylinder banks and a high-pressure injection system is provided for each cylinder bank.
The gasoline direct injection is carried out in a spark-ignition engine utilized in a motor vehicle with a high-pressure injection system. The high pressure, which is necessary for an optimal combustion in the cylinders, must be built up over a few seconds after each engine start. For this reason, the actual starting operation takes place at a significantly lower prepressure of the electric fuel pump.
For a cold start of the engine at low prepressure, there are however very large fuel quantities to be injected in order to ensure a reliable combustion. This combustion is however not optimal and a high consumption of fuel occurs with correspondingly high exhaust gas emissions. The first cold start injection operations ensure a very slow buildup of the high pressure because of the large fuel quantities which are taken from the high pressure rail. In the early start phase, the pressure in the high pressure rail lies even below the prepressure because of the pressure losses between the electric fuel pump and the high pressure rail.
The engine speed (rpm) during the first combustions increases rapidly. For this reason, the time shortens which is available for the subsequent injections. For this reason, the desired large fuel quantity cannot be timely injected in advance of the particular ignition. The corresponding smaller injected fuel quantity does not combust reliably and misfires can occur with a corresponding deterioration of the composition of the exhaust gas. In this way, a continuous increase in rpm is prevented and the engine speed alternately collapses and increases until the rpm is stable after several seconds and the start operation is ended.
It is an object of the invention to provide a method for a rapid and reliable engine start of gasoline direct injection internal combustion engines having several cylinder banks in that the above-described deficiencies such as the slow buildup of the high pressure, high fuel consumption, high exhaust-gas emissions and the problem of misfires are reduced or are avoided.
The method of the invention is for starting an internal combustion engine operated with direct injection including an engine for a motor vehicle, the engine being subdivided into several cylinder banks with high-pressure injection systems being provided for corresponding ones of the cylinder banks. The method includes the steps of: injecting each of the cylinders of a first one of the cylinder banks in a first phase (A) while not injecting the cylinders of the remaining one(s) of the cylinder banks; and, in a subsequent second phase (B), injecting those cylinders of a second one of the cylinder banks.
The advantage of the invention is that the start operation is first initiated only on one cylinder bank with fuel prepressure in an internal combustion engine having gasoline direct injection and having several cylinder banks with each cylinder bank having a high pressure system. Thereafter, the other cylinder banks can be switched in at higher fuel pressure.
The method according to the invention includes the embodiments presented below.
Basically, for each type of engine, an individual determination can be made as to whether or when each individual injection valve should inject during a cold start phase.
In a multi-bank engine, an injection once or several times into all cylinders of the first cylinder bank can take place and then once or several times into all cylinders of the remaining cylinder banks and thereafter into all cylinders of all cylinder banks in accordance with the normal ignition sequence. It can be individually determined which cylinder bank will be injected first and how the sequence of the injection will be for the remaining cylinder banks.
In a multi-bank engine and depending upon the requirements, one or several injections into all cylinders of a first cylinder bank takes place and thereafter into all cylinders in accordance with the normal ignition sequence. Here too, it can be individually determined which cylinder bank will be injected first.
In a multi-bank engine, and depending upon demand, injection can be sequentially into different cylinder banks and only thereafter into all cylinders of all cylinder banks in accordance with the normal ignition sequence. The sequence of the cylinder banks into which injection is to be made is in principle freely selectable or can be individually fixed depending upon the type of engine. Within this sequence, injection can also be made simultaneously into several cylinder banks.
Furthermore, the following can be fixed in a multi-bank engine: time point, frequency and sequence of the injections into individual cylinder banks in dependence upon the fuel high pressure measured in each case. If required, this can be individually determined in each starting operation.
In the method in accordance with the invention, the fuel high pressure system is subdivided in correspondence to the engine banks and an injection suppression strategy is executed for the cold start. In addition to this method of the invention, a variable rail volume or a variable pumping characteristic of the electric high pressure pump can contribute to a more rapid cold start and a more rapid high pressure buildup with a simultaneous lower fuel consumption and lower exhaust gas emission.
The realization of the method of the invention in the form of a control element is of special significance. The control element is provided for a control apparatus of an internal combustion engine and especially for a motor vehicle. A program is stored on the control element and is suitable for running on a computing apparatus and especially on a microprocessor and is suitable for executing the method of the invention. In this case, the invention is realized by a program stored on the control element so that this control element, which is provided with the program, defines the invention in the same way as the method for which the program is suitable for executing. Especially an electric storage medium can be used as a control element, for example, a read-only-memory.